Semantic Web Architecture

Before we proceed with an overview of the Semantic Web Architecture, let us first define the goals of the Semantic Web:

  • Consistent Knowledge – Knowledge about a specific thing  is consistent across distributed knowledge sources. Any knowledge change should be reflected across all mutually dependent knowledge sources.
  • Accessing Knowledge – Providing the most accurate knowledge aggregated from all available sources.
  • Reusing Knowledge – Knowledge can be fully internally and/or externally reused  by having it formally structured and open.

Architectural Principles

An architecture is a model of a system that is defined within a certain context. The model is an abstraction of a real world representation.  The context defines a view of appraisal of the system. It also determines the components necessary to implement the system, the properties of these components, the relationships between the components, and relationships with external entities.

The layered architecture is an architectural pattern widely used today to present conceptual Semantic Web Architecture.  Generally in a layered architecture, the components of the system are arranged in a layered structure where each layer represents a group of elements providing related services. There are two types of this architecture: open and closed. In the open architecture, higher layers can use all or subset of services from all lower layers. In the closed architecture a higher layer can use only service from the immediate lower layer. In both type of the layered architecture lower layers cannot use services from higher layers.

A typical widely used layered architecture is ISO/OSI (International Standards / Open Systems Interconnect) architecture [1]. This architecture specifies functional foundation needed to define protocols for network interoperability between applications.  The Semantic Web architecture has the same purpose as ISO/OSI architecture in that it specifies the languages required for data interoperability between applications.

The context of the Semantic Web Architecture are languages required for meta-data specifications and reasoning about information (knowledge) specified via the meta-data specifications.

Towards Technology Agnostic Conceptual Semantic Web Architecture

A precise definition of architectural layers’ functionalities and their interfaces has to be provided for the Semantic Web applications to interoperate.

Gerber at al. [2] defined Comprehensive, Functional, Layered (CFL) architecture for the Semantic Web. This architecture is based on the previous versions of the Semantic Web Architecture defined by Tim Berners-Lee [3,4,5,6,7,8,9].  It defines related Semantic Web functionalities rather than the W3C technologies as the architectural layers. The CFL architecture enables use of different technologies to implement the functionality of a specific layer. However the specification of the functionality interfaces needed to clearly define interfaces between the layers has not been defined yet.

The CFL architecture proposes two orthogonal architecture stacks, the language stack and the security stack (Fig. 1).

Figure 1: CFL Architecture

The Layers of the CFL Semantic Web Architecture

The layers of the CFL architecture include:

Unicode Identification Mechanism

Used to uniquely identify resources. It also provides a mechanism for uniquely identifying all the characters in all written languages. Examples of this layer technologies are: Unicode [10]and Uniform Resource Identifier (URI)  [11,12,13].

Syntax Description Language

Provides a language for specifying syntax of various data formats. The most used technologies include XML [14], XML Schema [15], and Namespaces [16].

Meta-data Data Model

Provides a mechanism to model the meta-date required to implement the Semantci Web. The most used technologies for this layer include: RDF and RDF Schema (RDFS) [17].


This layer provides language support for creation of ontologies. It is instantiated with either RDFS or RDFS and OWL [18].


This layer belongs to rule-based languages and their processing. Rule Interchange Format (RIF) is the W3C rule-based  language and it is compatible with RDF and OWL [19]. There is also an important group of rule-based languages [20] that cannot be layered on top of OWL. They should be also included in the Semantic Web Architecture together with other RDF and OWL related rule-based languages. I will review these languages in one of the future posts. In addition to allow query and filtering the rules layer also supports inference.

Logic Framework

This layer provides an answer about the reasoning of why the information is taken or appear to the user. Currently the technology specification for this layer does not exist.


Thids layer provides an answer for the question of why agents should believe the provided information.  Currently the technology specification for this layer does not exist. The Knowledge Systems Laboratory  at Stanford has been developing a proof language called PML [21]


This layer ensures that he information provided is valid and there is a degree of confidence in the resource that provides the information . Currently the technology specification for this layer does not exist.

Identity Verification and Encryption

This layer belongs to security (especially identification and encryption at least).  It is not part of the language stack. It should be developed as a separate Security Architecture that will interface with the language stack. The W3C technology specs that belong to this layer are XML Signature [22] and XML Encryption [23].


1. OSI Reference Model – The ISO Model of Architecture for Open Systems Interconnection
Hubbert Zimmerman

2. A Functional Semantic Web Architecture
Aurona Gerber, Alta van der Merwe, and Andries Barnard, 2008

3. Semantic Web – XML2000. W3C Web site 2000
Tim Berners-Lee

4. WWW2005 Keynote. W3C Web site 2005
Tim Berners-Lee,

5. Artificial Intelligence and the Semantic Web: AAAI2006 Keynote. W3C Web site 2006
Tim Berners-Lee

6. The Semantic Web and Challenges. W3C Website Slideshow 2003
Tim Berners-Lee

7. Standards, Semantics and Survival. SIIA Upgrade 2003, pp. 6-10.
Tim Berners-Lee

8. WWW Past and Future. W3C Web site 2003
Tim Berners-Lee

9. SIIA. Website

10. Unicode

11. Designing URI Sets for the UK Public Sector, V1.0, October, 20009
Paul Davidson, CIO, Sedgemoor District Council

12. Cool URIs for the Semantic Web
W3C Working Draft, 17 December, 2007

13. Cool URIs dont’ change
Tim Berners-Lee

14. XML, W3C

15. XML Schema, W3C

16. Namespaces in XML 1.1, W3C

17. RDF Standards, W3C

18. OWL, W3C

19. RIF RDF and OWL Compatibility, W3C

20. A Realistic Architecture for the Semantic Web
Michael Kifer, Jos de Bruijn, Harold Boley, and Dieter Fensel

21. A Proof Markup Language for Semantic Web Services
Paulo Pinheiro da Silva, Deborah L. McGuinness, Richard Fikes

22. XML Signature, W3C

23. XML Encryption, W3C


Enterprise Information Architecture

Information Architecture (IA) models information and knowledge, and specifies architectural components and processes for information and knowledge management.

Some of the IA activities include:

  • Analyze processes that use and create information
  • Analyze information
  • Create data models, metamodels, taxonomies, ontologies, and other information modeling concepts to model information about physical and abstract things.
  • Analyze quality of data
  • Design user interfaces for managing information
  • etc.

There are two main types of IA:

  • Enterprise Information Architecture (EIA)
  • Large Scale Information Architecture (LSIA)

Enterprise Information Architecture (EIA) provides support for applications of information architecture in enterprises.  Information and knowledge is the foundation of any enterprise which EIA is responsible for. EIA has to operate in the context of enterprise processes.

Understanding of enterprise’s strategy and goals is an important factor for a successful application of EIA.

While it is based on the same principles as the EIA, LSIA besides the EIA common activities also addresses large scale issues mostly related to service oriented (free of charge or commercial) Internet applications that manage very large data sets that are concurrently accessed by the large number of users.


Why Is It Important to Understand Business Strategy and Goals?

Detailed understanding of the overall business strategy is one of the key factors of the successful EIA. Enterprise Architects conduct research to identify needs and issues from staff what is then used to identify goals and scope of the projects. Enterprise Information Architects should provide inputs into the business strategy development. These inputs belong to enterprise information and how its management affects the overall business strategy. Integrating business strategy into EIA is one of the important architectural aspects. Enterprise Information Architecture as its name says puts the enterprise not the specific project into the center of its scope. It provides an enterprise-centric model for modeling, managing, and analyzing enterprise information.

The business strategy of the enterprise should be based on detailed analysis of the enterprise processes and processes that shape current and future directions of the market the enterprise supports. This way the enterprise will make sure that it  understands the current functioning of its business in a context of the current market. Based on that, enterprises come up with strategies very much needed to clearly communicate the next direction(s) of the enterprise.

Strategic goals and business objectives are communicated by the senior management of the enterprise. Enterprise Information Architects and other architects have to make sure that these goals and objectives are fully supported and articulated in the architecture of enterprise systems that will be providing support for the business strategy implementations.

Why Processes are Important?

Processes are fundamental concepts of any architecture on any level. Everything is a product of a process. A process can be of any type (i.e., business process, manufacturing process, social process, political process, natural process, etc.). Besides the overall enterprise strategy and clear understanding of directions, Enterprise Information Architects need detailed understanding of processes they have to support to be able to properly model, use, manage, and analyze information created and controlled by these processes. It is important that the managed information is modeled from the process-based context rather than from the disconnected no process based pure non-empirical information context.

IA Framework

IA needs an Information Architecture Framework (IAF) that enables a full integration of information over projects and enterprise systems. IAF provides a common established methodology and tools to model, manage, integrate, and analyze information. Information can be in both structured and un-structured form. Best practices and standards are also part of the framework. IAF itself is agnostic to any specific type of information architecture (i.e., enterprise or large scale).

Measure Results

Enterprise information management projects based on a solid EIA have to demonstrate measurable results. Everything should end up with a successful implementation of information management to support enterprise strategies and meet goals of enterprises. All these strategies and goals are related to people either in an internal enterprise context or an external enterprise context in the enterprise’s dealing with customers and partners. Metrics to measure the success have to be developed as well